The  Structure  and  Parasitism  of  Aphyllon 

Unifloram,  Gray. 

( WITH  PI  A  TPS  XIII-XV') 

By  Amelia  C.  Smith,  B.  S. 

Aphyllon  unifiorum ,  or  the  Naked  Broom-rape,  belongs  to 
the  large  parasitic  order  of  the  Orobanchacece,  and  is  by  some 
included  in  the  genus  Orobanche .  It  is  typically  a  North 
American  species,  and  is  a  pure  parasite,  being  without 
chlorophyl.  The  present  study  was  undertaken  at  the  sug¬ 
gestion  of  Professor  Macfarlane,  and  was  carried  out  under  his 
direction.  All  of  my  material  has  been  collected  from  one 
very  limited  locality  at  Glenolden,  Pennsylvania,  where  it 
grows  luxuriantly.  It  appears  toward  the  end  of  May,  when 
Aster  plants  are  about  nine  inches  higl},  and  by  the  end  of  ' 

June  the  seeds  are  matured  and  the  plant  is  withering.  I  have 
invariably  found  it  parasitic  on  the  roots  of  Aster  corymb o sum. 

Chatin  states  that  it  is  parasitic  on  Solidcigo  and  other  Synan- 
therae,  while  Beck  gives  the  following  list  of  host-plants  : 

Species  of  Artemisia ,  species  of  Solidago ,  Sedum  stenopeta- 
lum  (!)  By  carefully  cutting  out  and  lifting  a  large  sod  con¬ 
taining  several  Asters  and  a  clump  of  Aphyllon ,  and  then 
washing  away  the  soil  until  the  roots  were  exposed,  I  was  able 
to  trace  the  root-connections  with  certainty. 

Methods. 

Some  of  my  material  was  killed  in  saturated  aqueous  solu¬ 
tion  of  corrosive  sublimate,  a  smaller  quantity  in  absolute 
alcohol,  and  a  great  deal  of  it  was  simply  preserved  by  plac¬ 
ing  it  at  once  in  70  per  cent  alcohol.  For  general  structure, 
all  of  the  above  methods  gave  equally  good  results.  For 

hi 


tiiOLOGl 


I  12 


Smith  071  Structure  and  Parasitism 


histological  detail,  and  for  embryological  study,  all  of  these 
methods  proved  equally  bad.  The  protoplasm  was  somewhat 
shrunken  even  in  the  best  specimens,  and  of  course  this  was 
especially  marked  in  the  macrospore  and  surrounding  cells  of 
the  ovule. 

General  Morphology. 

The  plant  is  of  a  pale  purplish-white  color,  and  attains  a 
height  of  from  four  to  five  inches.  The  roots  are  thick  and 
fleshy,  arise  in  clusters  from  the  base  of  the  stem  and  branch 
quite  freely  in  all  directions.  Roots  forming  parasitic  connec¬ 
tions  either  end  in  a  knob-like  sucker,  or  (as  is  more  usual) 
may  continue  past  the  sucker  and  end  as  a  soil-root.  Some¬ 
times  one  Aphyllon  root  forms  several  suckers  on  the  same  or 
on  different  Aster  roots.  The  soil-roots  are  more  numerous 
than  the  parasitic  ones,  and  from  the  structure  of  the  former 
it  seems  probable  that  they  are  functionless  as  absorbing 
agents,  and  serve  merely  as  hold-fasts. 

The  stem  is  short,  fleshy,  and  relatively  very  thick,  often 
more  than  one-quarter  inch  in  diameter,  and  from  one  to  one 
and  a  half  inches  in  length.  It  may  branch  several  times  at 
the  base,  or  may  remain  unbranched.  Foliage  leaves  are 
entirely  absent,  or  else  are  represented  only  by  one  or  two 
very  thin  scale-leaves  at  the  base.  The  bracts  are  the  con¬ 
spicuous  leaves  of  the  plant,  and  in  a  stout,  vigorous  speci¬ 
men  may  number  five  to  ten.  In  the  axils  of  the  upper  bract- 
leaves  are  developed  the  long,  hollow  scapes,  each  bearing  a 
single  irregular,  purplish-white  flower.  Upper  bract-leaves, 
scape  and  flower  are  thickly  clothed  with  glandular  hairs. 

I  have  found  no  trace  of  any  perennating  structure,  and 
the  plant  seems  to  be  strictly  an  annual. 

Structure  of  the  Roots. 

The  epidermis  is  of  flattened,  somewhat  thick-walled  cells. 
Some  contain  globules  of  a  peculiar  oil-like  substance,  but  it 


Of  Aphyllon  Uniflorum ,  Gray.  1 1 3 

is  not  uniformly  present,  and  some  of  the  cortical  cells  show 
it  also.  I  have  found  no  trace  of  a  symbiotic  fungus  in  the 
epidermis. 

Beneath  the  epidermis  is  the  cortex,  some  ten  or  twelve 
cells  deep.  These  cells  contain  many  small,  rounded  starch 
grains,  which  are  usually  placed  on  the  lower  and  inner  sides 
of  the  cell.  Chatin  states  that  the  epidermis  contains  fine 
granules,  and  the  parenchyma  large  granules,  “ni  verts  ni 
amylaces,”  but  Koch  states  that  starch  is  invariably  present  in 
the  roots  of  Ovobanche.  Chatin  may  possibly  have  reference 
to  the  oil-like  globules  mentioned  above. 

Within  the  cortex  is  a  reduced  and  degenerate  bundle-sys¬ 
tem.  The  bundle-sheath  is  quite  absent  in  some  roots,  in 
others  it  is  represented  in  patches.  The  arrangement  of  wood 
and  bast  varies  considerably.  It  is  most  commonly  diarch. 
A  modification  of  this  is  found,  in  which  the  wood  projects 
on  one  side  of  the  bundle,  so  that  the  phloem  of  that  side  is 
subdivided.  A  smaller  proportion  show  a  triarch  arrange¬ 
ment,  while  in  some  there  seems  to  be  an  indiscriminate  dis¬ 
tribution  of  wood  elements.  The  xylem  consists  of  rather 
short,  pitted-reticulate  elements,  and  though  less  in  bulk  than 
the  phloem,  is  better  differentiated.  The  phloem  is  composed 
of  elongated  elements,  filled  with  highly  granular  contents,  in 
which  nuclei  frequently  persist.  Sieve-tubes  seem  to  be 
entirely  absent.  Protoplasmic  connections  between  the  cells 
corresponding  functionally  in  all  probability  to  similar  pro¬ 
cesses  in  sieve-tubes  were  sometimes  observed. 

Root-hairs  are  either  entirely  absent,  or  are  doubtfully  rep¬ 
resented  by  a  few  small,  widely  scattered,  dermal  papillae. 
Absorption  must  therefore  be  impossible  for  these  roots.  This 
is  in  harmony  with  Koch’s  statement  as  to  the  total  absence 
of  root-  hairs  in  Orobanche  speciosa ,  0.  minor ,  0.  ram  os  a , 
and  0.  Hederce ,  which  he  studied  embryologically.  Koch 
finds  a  root-cap  on  the  soil-roots,  i.  e.,  the  secondary 
8 


1 1 4  Smith  071  Structure  ci7id  Parasitis7)i 

roots  of  the  above-mentioned  species  of  Orobaiiche.  They 
do  not  seem  to  be  present  in  Aphyllo7i ,  but  as  I  have  not 
obtained  any  very  young  stages,  it  is  possible  that  the  root- 
caps  are  formed  here  also,  and  later  slough  off. 

Parasitic  Connections. 

Parasitic  connection  with  the  host  is  effected  by  large 
haustoria,  which  fasten  upon  the  host-root.  The  Aster  roots 
are  usually  less  than  half  the  diameter  of  the  AphylloTi  root,  but 
are  harder  and  more  woody.  As  a  rule,  they  are  not  shriveled 
beyond  the  point  of  contact,  but  pass  through  the  cluster  of 
Aphyllon  roots  and  enter  the  soil  beyond  them.  The  host- 
root  is  not  completely  surrounded  by  the  sucker,  but  usually 
remains  distinct  and  quite  unmodified  in  structure  on  the  side 
away  from  the  parasite.  The  sucker  is  covered  with  an 
epidermal  layer  similar  to  that  over  ordinary  Aphyllo7i  roots, 
and  this  is  quite  continuous  with  the  epidermis  of  the  host- 
root.  Beneath  the  epidermis  the  haustoria  are  composed  of 
parenchymatous  tissue,  with  strands  of  bundle-tissue,  which 
branch  almost  at  right  angles  from  the  bundle-tissue  of  the 
main  root.  This  parenchyma  spreads  and  mingles  with  the 
parenchyma  of  the  host  so  intimately  that  it  is  impossible  to 
distinguish  their  boundaries  (Plate  XIV,  Fig.  2).  The  xylem 
and  phloem  elements  of  the  parasite  pass  into  the  xylem  and 
phloem  regions  of  the  host,  and  mingle  with  the  correspond¬ 
ing  elements  of  the  host-bundle.  The  general  position  of  the 
bundle  of  the  host,  is  little  modified  however,  and  there  seems 
to  be  no  separation  and  isolation  of  bundle  elements  from  the 
host-root  within  the  tissue  of  the  parasitic  tubercle,  such  as 
occurs  in  Conopholis. 1 

1  L.  L.  W.  Wilson,’  Observations  on  Conopholis  Americana,  Bot.  Contrib. 
Univ.  Penn.,  vol.  ii,  p.  12. 


Of  Aphyllon  Uniflorum,  Gray. 
Structure  of  the  Stem. 


i  1 5 


In  cross  section  the  stem  shows  an  epidermis  of  small 
flattened  cells,  thick-walled  on  the  outer  side  (Plate  XIV, 
Fig.  3).  Beneath  is  the  cortex,  composed  of  large,  rounded 
cells  ;  there  are  usually  from  eight  to  ten  layers  of  these  cells, 
although  the  stems  vary  considerably  in  this  respect.  The 
cortical  cells  are  closely  packed  with  large  rounded  starch 
grains.  Within  is  a  more  or  less  continuous  ring  of  degen¬ 
erate  bundles,  widely  separated  in  some  places  by  medullary 
rays.  Within  the  bundle-ring  again  is  the  pith,  its  large 
rounded  cells  packed  with  starch  grains. 

The  bundles  are  arranged  in  the  usual  manner,  with  exter¬ 
nal  phloem  and  internal  xylem.  A  reduced  bundle-sheath  is 
present  as  a  frequently  interrupted  ring  of  small  rounded  cells. 
The  phloem  consists  of  elongated  elements  with  granular 
contents,  which  are  sometimes  nucleated.  As  in  the  root, 
sieve -tubes  seem  to  be  entirely  absent.  The  protoxylem  con¬ 
sists  of  one  or  two  spiral  tracheae  with  cells.  The  secondary 
xylem  consists  of  short  pitted-reticulate  tracheae,  strongly 
indurated.  A  cambium  is  not  generally  present,  although 
some  stems  show  interrupted  lines  of  small  cells  which  may 
doubtfully  be  interpreted  as  cambium.  Although  the  xylem 
elements  are  fairly  numerous  in  root  and  stem,  it  seems  prob¬ 
able  that  the  wood  has  nothing  to  do  with  the  conduction  of 
nutritive  liquids,  but  serves  solely  to  support  and  strengthen 
the  plant. 

The  presence  of  such  quantities  of  starch  in  a  colorless 
parasitic  plant  is  somewhat  perplexing.  The  starch  cannot 
have  been  brought  over  from  the  host  as  such,  since  starch 
is  insoluble,  so  that  leucoplasts  must  be  present,  and  in  con¬ 
siderable  numbers.  They  are,  however,  small  and  difficult  to 
make  out  clearly.  Moreover  it  is  puzzling  to  see  such  an 
amount  of  reserve  food  stored  in  all  parts  of  a  purely  annual 


1 1 6  Smith  on  Structure  and  Parasitism 

plant.  Koch  states  that  the  large  amount  of  starch  stored 
up  in  a  young  plant  immediately  after  germination,  is  to  insure 
it  against  starvation  in  case  the  host  perishes.  But  starch  is 
present  in  great  quantities  when  the  seeds  are  nearly  or  quite 
ripe,  and  it  is  passed  into  the  soil  with  decay  of  the  plant. 
It  can  scarcely  be  wholly  to  insure  a  supply  for  the  endosperm, 
for  the  amount  stored  there  is  infinitesimal  compared  to  that 
in  the  entire  plant.  Further,  the  conditions  of  germination 
preclude  the  possibility  that  the  starch  is  present  in  order  that 
the  seeds  may  find  a  rich  nidus  in  the  decaying  parent  plant. 

Bract-Leaves. 

The  bract-leaves  are  thick  at  the  base,  gradually  thin  out 
at  the  top,  and  are  closely  appressed  to  the  stem.  The  epi¬ 
dermal  cells  are  small  and  flattened.  The  mesophyll  is  packed 
with  starch,  and  is  supported  by  a  few  strands  of  bundle- 
tissue,  which  enters  the  bract  as  one  strand,  and  quickly  sub¬ 
divides.  The  tips  of  these  leaves  are  very  slightly  trifid,  a 
fact  that  perhaps  points  to  a  three-lobed  ancestral  leaf.  The 
lower  bract-leaves  differ  markedly  from  the  upper.  The 
lower  ones  have  neither  stomata  nor  hairs.  The  upper  ones 
have  numerous  stomata  on  the  free  outer  (morphologically 
under)  surface,  and  the  tips  and  outer  surfaces  are  clothed 
with  multicellular,  capitate  hairs.  Between  these  two  extremes, 
selecting  a  plant  with  five  leaves,  there  are  transitional  stages. 

The  Flower. 

The  flower  is  irregular,  produces  a  five-parted  calyx,  a  five- 
parted  bilabiate  corolla,  four  epipetalous  stamens,  and  a  superior 
bicarpellate  ovary.  Bracteoles  are  absent.  The  calyx  is 
almost  or  quite  regular.  Its  lobes  are  fleshy  and  bear  hairs 
on  the  outer  surface.  The  epidermis  consists  of  irregular 
cells  of  wavy  outline,  and  is  pierced  with  many  stomata.  The 


Of  Aphy lion  Uniflorum ,  Gray.  117 

bundle-strands  enter  each  lobe  singly,  but  immediately  divide 
into  three  main  branches. 

The  upper  lip  of  the  tubular  corolla  consists  of  two  some¬ 
what  recurved  lobes,  the  lower  of  three  lobes.  Each  lobe  is 
supported  by  two  main  strands  of  bundle-tissue,  which  enter 
separately  as  branches  of  the  bundle-ring  in  the  floor  of  the 
flower.  The  outer  surface  of  the  corolla  bears  many  hairs 
above  the  line  where  the  calyx  lies  against  it,  the  inner  surface 
not  nearly  so  many.  These  hairs  are  all  of  the  same  type, 
having  a  stalk  of  several  cells  placed  end  to  end,  and  a  round 
head  formed  of  (usually)  eight  radially  arranged  cells.  The 
four  epipetalous  stamens  are  didynamous,  the  posterior  pair 
being  the  shorter.  The  anther-lobes  are  formed  in  the  usual 
way,  having  at  first  four  and  later  two  loculi.  The  micro¬ 
spores  are  small  and  spherical. 

The  unilocular  ovary  consists  of  antero-posterior  carpels. 
Externally  it  is  quadrangular  in  shape,  corresponding  to  the 
positions  of  the  four  placentas,  and  the  style  bends  forward 
so  that  the  broad  bilobed  stigma  lies  at  the  anterior  part 
of  the  mouth  of  the  flower-tube.  At  the  base  of  the  ante¬ 
rior  carpel  is  a  large  nectary  sunk  into  the  tissues  of  the 
carpel  (Plate  XV,  Fig.  7).  In  cross  section  the  ovary  shows 
an  epidermal  layer  of  high  columnar  cells,  the  outer  walls  of 
which  are  thickened.  Within  are  several  (four  or  five)  layers 
of  rounded  cells.  The  four  parietal  placentas  are  cushion-like 
ingrowths  of  similar  rounded  cells,  the  entire  ovarian  wall  being 
packed  with  starch.  A  well-marked  bundle-strand  is  present 
in  the  middle  of  each  carpel,  the  position  of  the  bundle  being 
indicated  externally  by  anterior  and  posterior  grooves  on  the 
surface  of  the  ovary.  The  small  anatropous  ovules  are  pro¬ 
duced  in  great  numbers  (Plate  XIV,  Fig.  4). 

The  nectary  shows  in  cross  section  seven  to  nine  layers  of 
gland  cells,  which  are  readily  distinguishable  by  their  small 
size,  rounded  outline,  the  absence  of  starch,  their  granular, 


1 1 8  Smith  on  Structure  and  Parasitism 

rather  deeply-stained  protoplasm,  and  large  conspicuous  nuclei. 
In  the  middle  of  the  nectary,  these  cells  extend  quite  to  the 
bundle-ring,  but  on  each  side  there  is  a  rapid  transition  to  the 
parenchyma  of  the  carpellary  walls.  There  is  no  special 
covering  of  epidermal  cells  over  the  nectary  (Plate  XV, 
Fig.  7).  Externally,  the  gland  appears  as  a  small,  rounded 
whitish  swelling  at  the  base  of  the  ovary.  The  presence  of 
this  gland  seems  to  have  been  overlooked  by  Chatin,  for  he 
characterizes  the  genus  as  one  in  which  the  ovary  is  unaccom¬ 
panied  by  an  hypogynous  gland. 

Structure  and  Development  of  the  Ovule  and  Seed. 

The  mature  seed,  which  is  very  small  and  light,  is  sur¬ 
rounded  by  a  tough,  leathery  coat,  whose  flattened  cells  have 
thickened  indurated  walls.  The  seed  itself  consists  of  a  mass 
of  endosperm  cells,  packed  with  starch,  and  enclosing  a  small 
primitive  embryo  whose  cells  contain  little  or  no  starch. 
The  embryo  is  undifferentiated  into  plumule,  cotyledons  or 
radicle.  These  seeds  will  not  germinate  in  water,  nor  in  a 
nutrient  solution  made  from  the  bruised  roots  of  the  host. 
Koch  states  absolutely  that  the  seeds  of  0.  speciosa,  0.  ramosa , 
0.  minor ,  0.  Hederce  must  come  in  contact  with"  the  host-root 
if  they  are  to  germinate,  and  Meehan  finds  the  same  for 
A  phyllon. 

I  have  not  yet  worked  out  entirely  the  development  of  this 
seed  from  the  young  ovule,  and  between  Figs.  2  and  3  (Plate 
XV),  I  have  as  yet  no  certain  connecting  links.  Fig.  1  shows 
the  first  appearance  of  the  macrospore-mother-cell  in  very 
young  ovules.  The  ovule  is  here  still  orthotropous,  and  is  a 
small  conical  upgrowth,  covered  with  one  layer  of  cubical 
cells  and  containing  a  large  macrospore-mother-cell.  Fig. 
2,  shows  an  older  ovule.  The  ovule  has  here  turned 
through  an  angle  of  nearly  90  degrees.  The  macrospore- 
mother-cell  has  greatly  elongated,  and  is  surrounded  by 


Of  Aphyllon  Uniflorum ,  Gray.  119 

a  clearly-marked  nucellus,  while  the  primine  has  grown 
nearly  around  the  nucellus.  Up  to  this  stage  there  has 
been  clearly  no  formation  of  tapetal  cells,  and  (although  my 
material  was  too  badly  shrunken  to  be  very  satisfactory)  I  have 
reason  to  doubt  their  formation  at  any  time.  I  have  observed 
many  completely  anatropous  ovules,  which  contained  within 
the  three  cell  layers  one  much  elongated,  darkly-staining 
mass  of  protoplasm.  Many  of  these  showed  two  nuclei,  but 
a  clear  unmistakable  transverse  wall  could  not  be  observed. 
Koch,  in  his  “  Entwicklungsgeschichte  der  Orobanchen,” 
figures  for  0.  speciosa  the  division  of  the  macrospore-mother¬ 
cell  into  four,  of  which  the  upper  one  is  the  macrospore  ;  and 
this  division  occurs  when  the  ovule  is  turned  half-way.  If 
the  macrospore-mother-cell  does  divide  in  Aphyllon ,  the  divi¬ 
sions  must  occur  at  a  much  later  period  than  they  do  in  the 
related  species  described  by  Koch. 

Plate  XV,  Fig.  3,  shows  a  much  older  ovule.  The  integu¬ 
ments  fully  surround  the  nucellus,  and  the  outer  one  is  closely 
packed  with  starch,  while  the  nucellus  is  pressed  against  by 
the  structures  within.  Owing  to  the  lack  of  closely  preced¬ 
ing  stages  this  ovule  cannot  be  interpreted  with  complete  cer¬ 
tainty  as  yet.  The  probable  interpretation,  based  upon  the 
development  of  related  plants,  is  as  follows  :  The  multicellular 
cell-body  represents  the  mass  of  precociously  developed 
endosperm,  which  has  grown  up  around  the  egg-cell  into  a 
neck-like  structure.  The  central  cell  is  the  egg,  still  unseg¬ 
mented,  and  the  long,  plug-like  body  filling  the  apparent  neck, 
is  the  suspensor,  consisting  of  two  cells.  At  the  opposite 
end  of  the  ovule,  one  cell  represents  the  remnant  of  the 
antipodal  cells,  which  have  become  shrunken.  Such  forma¬ 
tion  of  precocious  endosperm  is  common  throughout  the 
Orobanchacece ,  and  in  Aphyllon  it  seems  to  take  place  to  a 
greater  degree  than  in  O.  speciosa ,  as  described  by  Koch, 
where  the  neck-like  upgrowth  of  the  endosperm  around  the 
suspensor  is  much  less  perfectly  developed  than  in  Aphyllon. 


120 


Smith  on  Structure  and  Parasitism 


Plate  XV,  Fig.  4,  shows  the  stage  immediately  following. 
The  egg  has  divided  longitudinally,  and  the  suspensor  consists 
of  four  cells.  The  lowest  of  these  is  destined  to  become  the 
hypophysis  of  the  future  embryo. 

In  Fig.  5  the  egg  has  divided  into  octants,  and  the  hypophysis 
is  plainly  marked.  The  suspensor  is  still  four-celled.  The 
endosperm  has  increased  greatly  in  bulk,  and  numerous  small 
starch  grains  are  found  in  its  cells. 

Fig.  6,  of  Plate  XV,  illustrates  an  almost  mature  seed. 
The  integuments  have  become  thin  and  flattened,  and  the  endo¬ 
sperm  contains  much  starch.  The  embryo  has  attained  its 
full  development.  The  regions  are  not  clearly  marked  out, 
but  the  hypophysis  here  shows  only  anticlinal  divisions.  This 
is  in  harmony  with  Koch’s  statement  that  the  primary  root 
forms  no  root-cap. 

Summary. 

1.  Aphyllon  uniflorum  is  parasitic  on  Aster  corymbosum. 
The  degeneration  attendant  upon  its  parasitic  habit  is  expressed 
by : 

( a )  Absence  of  chlorophyl. 

( 'b )  Degeneration  of  bract-leaves. 

( 'c )  Loss  of  root-hairs. 

( d)  Reduction  of  the  bundle-system,  and  the  greater 

relative  development  of  phloem  than  of  xylem. 

(e)  Small  size  of  seed  and  primitive  embryo,  and  the 

development  of  this  embryo  within  a  mass  of  pre¬ 
cocious  endosperm  which  completely  surrounds 
the  embryo  and  suspensor. 

2.  Parasitic  roots  form  intimate  connections  with  host-roots, 
but  the  host-roots  are  not  entirely  starved  beyond  the  point 
of  attachment. 

3.  Stomata  are  present  on  bract-leaves,  flower-stalk,  calyx 
and  corolla. 


Of  Aphyllon  Uniflorum,  Gray. 


1 2 1 


4.  A  well-developed  ovarian  nectar-gland  is  present. 

5.  Starch  is  present  in  great  quantities  in  roots,  stems, 
leaves  and  carpellary  tissue. 

BIBLIOGRAPHY. 

Beck  von  Managetta,  Monographic  der  Gattung  Orobanche.  (1890.)  Bibl.  Bot., 
Heft  19. 

Baillon,  Hist,  des  Plantes.  (1891.) 

Chatin,  Anatomie  Comparee  des  Vegetaux,  Plantes  Parasites.  (Paris,  1892.) 
Gray,  Asa,  Flora  of  N.  A. 

Koch,  Entwicklungsgeschichte  der  Orobanchen.  (Heidelberg,  1887.) 

Meehan,  Thos.,  Proc.  Acad.  Nat.  Sci.,  1881.  Part  II.  Pp.  160-162. 

Wilson,  Lucy  L.  W.,  Observations  on  Conopholis  Americana.  Contributions 
from  Bot.  Lab.  of  U.  of  P.,  Vol.  II,  p.  3. 

EXPLANATION  OF  PLATES  XIII,  XIV  AND  XV. 

Plate  XIII,  Plant  of  Aphyllon  growing  on  Aster  corymbosum. 

Plate  XIV,  Fig.  I.  L.  S.  Root  of  Aphyllon. 

Fig.  2.  T.  S.  Root  of  Aphyllon ,  forming  parasitic  connection  with  root-tissues 
of  Aster. 

Fig.  3.  T.  S.  Stem  of  Aphyllon. 

Fig.  4.  T.  S.  Ovary  of  Aphyllon ,  showing  placental  tissue  with  ovules. 

Plate  XV,  Figs.  X,  2.  Developing  ovules  of  Aphyllon. 

Fig.  3.  Mature  ovule,  containing  precocious  endosperm  and  egg  cell. 

Figs.  4,  5.  Upper  part  of  endosperm  surrounding  segmenting  egg  cell. 

Fig.  6.  Macrospore  enclosing  endosperm  and  multicellular  embryo. 

Fig.  7.  T.  S.  Nectary. 


The  Comparative  Structure  of  the  Flowers  in 
Polygala  polygama  and  P.  pauciflora, 
with  a  Review  of  Cleistogamy. 

( WITH  PLATES  XVI-XVII.) 

By  Charles  Hugh  Shaw,  Ph.  D., 

Professor  of  Botany  in  Temple  College. 


[Submitted  to  the  University  of  Pennsylvania  in  Partial  Fulfillment  of  the  Requirements  for 

the  Degree  of  Doctor  of  Philosophy.] 

In  the  genus  Polygala  only  two  species,  so  far  as  known, 
exhibit  cleistogamy.  Both  are  natives  of  the  Eastern  United 
States.  One  is  P.  polygama ,  often  abundant  along  our  sandy 
coasts,  the  other  is  P.  paucifolia ,  the  beautiful  so-called 
Flowering  Wintergreen  of  more  interior  districts. 

The  former,  alike  from  the  abundance  of  the  cleistogamic 
flowers  it  produces,  and  the  presence  of  intermediate  types 
now  for  the  first  time  described,  has  been  the  chief  subject  of 
the  present  study  and  will  be  first  dealt  with. 

The  detailed  description  of  the  various  types  of  flower  may 
best  be  prefaced  by  recapitulating  what  is  known  of  the 
flowers  of  the  genus. 

Conspicuous  blooms  are  borne  by  all  members  of  the 
genus.  These  are  generally  in  racemose  clusters,  and  are 
sometimes  very  showy.  The  typical  aerial  flower  is  very 
irregular.  In  the  calyx  the  two  lateral,  interior  sepals  are 
greatly  developed  as  petaloid  wings.  The  corolla  consists 
of  three  petals,  one  anterior  and  two  posterior,  the  two  lateral 
of  the  theoretical  five  being  suppressed.  Of  the  three  the 
anterior  one  is  greatly  developed  as  a  hood  covering  the 
stamens  and  pistil.  The  stamens  are  eight  in  number, 
the  anterior  and  posterior  ones  of  the  theoretical  ten  being 
wanting.  They  are  monadelphous,  being  united  below,  and 


122 


Vol.  II,  Plate  XIII.  Bot.  Contrib.  Univ.  Penn. 


Smith  on  Aphyllon. 


Vol.  II,  Plate  XIV 


Bot.  Contrib.  Univ.  Penn 


Fig.  3. 


Smith  on  Aphyllon 


Fig.  4. 


Vol.  1 1,  Plate  XV 


Bot.  Contrib.  Univ.  Perm. 


Fig.  3. 


Smith  on  Apiiyllon 


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